The invention relates to a small size zoom lens.
A zoom lens is known in the prior art which comprises a pair of front diverging group of lenses and a rear converging group of lenses and in which the magnification is changed by varying the spacing between the front and the rear group. While this lens is advantageous for the construction of a zoom lens including a wide angle region because of its inverted telephoto type arrangement, it suffers from the disadvantages that distortion increases in the negative sense toward a shorter focal length in which the separation between the front and the rear group becomes greater and that a spherical aberration degrades toward the longer focal length where the front and the rear group come close to each other.
A zoom lens of this type including seven individual lenses is disclosed in Japanese Laid-Open patent application No. 083,543/1976, for example. The proposed zoom lens has an aperture ratio of 1:2.8 which affords a sufficient brightness, but leaves something to be improved in the spherical aberration and coma. The distortion at the maximum focal length is high, and on the order of about -5%. Another zoom lens is disclosed in Japanese Laid-Open patent application No. 060,246/1978, but cannot be defined as including a wide angle region inasmuch as the maximum angle of view at the minimum focal length is as low as 54 degrees. In addition, the aperture ratio at the greater focal length is relatively low i.e., in the order of 1:4.5, which is attributable to the difficulty of correction of the spherical aberration toward the longer focal lengths. This results in a reduced brightness.